Sinn Féin leader Mary Lou McDonald has said that if there is a hard Brexit then it will "the imperative" that a Border poll on the constitutional future of Northern Ireland takes place.
She said, "Should there be a crash, and should there be the consequences of the crash, the hardening of the Border, the undermining of the Good Friday Agreement, robbing citizens of the basic rights, of course the constitutional question would have to be brought.
"No one should imagine that Theresa May's government could crash the North against the democratic wishes of the people out of the European Union, 'cause all of that jeopardy and all of that damage and not put the constitutional question. That would absolutely be a non-runner."
Taoiseach @campaignforLeo says now is "definitely" not the time to have a Border poll on a United Ireland. It would "very divisive"and see people breaking down along "religious and sectarian grounds." pic.twitter.com/WhbYOEhn0c— Conor McMorrow (@ConorMcMorrow) July 31, 2018
Speaking to the media this afternoon, she added that she had put this very directly to British Prime Minister Theresa May and her government.
Ms McDonald said it is not an ideal scenario nor the ideal climate for a referendum and she will work to create different conditions.
But if a crash happens, she said, "well then we have to play the hand we are dealt and that would make it as a matter of urgency that the question of Irish unity be put" to the people.
"Let me emphasise that would not be the ideal scenario. The ideal way to approach all of this is with a sense of urgency and purpose to engage all shades of opinion, for the Government in Dublin to lead in the planning and discussion of what United Ireland would look like and for unionism to take its place."
She said: "We will consider every single proposal on every issue, on the symbolic issues and on the bread and butter issues."
She said that the constitutional question needs to be put to a vote and Sinn Féin had said at the last Westminster election that it envisages a five-year timeline.
The Taoiseach has said that now is "definitely" not the time to have a Border poll.
Leo Varadkar said the indications are that if such a poll on a United Ireland did take place now it would be defeated.
"Some opinion polls have been closer than others but they have all indicated that a Border poll on a United Ireland would be defeated in Northern Ireland and it would be very divisive.
"So I don't see how that would be something welcome when it would be divisive and see people breaking down very much along religious and sectarian grounds. I don't think anybody wants that to happen.
"I also think in the current context it is just not helpful to be talking about Border polls and a United Ireland.
"There is real political instability in Northern Ireland and that is created by all the uncertainty about Brexit and what that means. The Northern Ireland Assembly and Executive are not operating and I don't think now is the time for us to get into that space."
Mr Varadkar added that "we need to give people clarity around Brexit. We need to get the Northern Ireland Assembly and Executive up and running, powersharing working and that is all about respecting the primacy of the Good Friday Agreement."